1. Field of the Invention
The present invention relates to a hydraulic/electric combination type rotation control device for a working machine of simultaneously using a hydraulic action by a hydraulic actuator and a rotation action by an electric motor.
2. Description of the Related Art
THE RELATED ART will be described taking an excavator as an example.
The excavator is, as shown in FIGS. 7 and 8, is configured such that an upper rotating body 2 is rotatably mounted on a crawler type lower traveling body 1 around a vertical axis O. On the upper rotating body 2, is installed an excavating attachment A provided with a boom 3, an arm 4, a bucket 5, a boom cylinder 6, an arm cylinder 7, and a bucket cylinder 8.
Instead of a total hydraulic drive method in which all the actions are performed by a hydraulic actuator driven by a hydraulic pump in the excavator, as proposed in WO2006/004080A1 (hereinafter, referred to as Patent Document 1), there is a hydraulic/electric combination method in which a rotation action is performed by an electric motor (rotation motor) and other actions are performed by the hydraulic actuator driven by the hydraulic pump as in the past. Hereinafter, as necessary, an excavator using the total hydraulic drive method is called as a total hydraulic excavator, and an excavator using the combination method is called as a combination excavator.
In the combination excavator, since the rotation action is independently performed by the electric motor and not influenced by a hydraulic action, movement which is different from the total hydraulic excavator is generated at the time of a combined operation for simultaneously performing the rotation action and the hydraulic operation.
As a representative example, at the time of a combined operation of rotating and boom raising for raising the boom 3 while rotating, in the total hydraulic excavator, since a oil supply amount to a rotation motor (hydraulic motor) is decreased by raising the boom, rotation speed is reduced and a degree of speed reduction is changed in accordance with a boom raising operation amount.
Therefore, there is a problem that an operator who is accustomed to such movement of the total hydraulic excavator feels uncomfortable with the movement of the combination excavator in which the rotation speed is not changed at the time of the combined operation, and operability is bad at this point.
It should be noted that in Patent Document 1, in order to deal with the problem of uncomfortableness due to the fact that the rotation speed is not changed relative to a change of a rotation rate of an engine, the rotation speed is changed in accordance with the rotation rate of the engine so as to perform control for imitating the movement of the total hydraulic excavator.
Therefore, by applying the technique, it is possible to control the rotation motor so that the rotation speed is reduced in accordance with for example the boom raising operation amount at the time of the combined operation of rotating and boom raising.
However, as a rotation property of the total hydraulic excavator at the time of the combined operation, pressure is lowered at the same time as a decrease in an oil amount supplied from the pump to the rotation motor so that acceleration is slowed down and the speed is reduced. Therefore, even if feedback speed control for eliminating deviation between target speed and actual speed is performed, the speed would only reach a target value at the end but it is not possible to obtain a move or sense of the “slow down of acceleration”.
Particularly, at the time of the combined operation of rotating and boom raising, a change in the oil supply amount to the boom cylinder is large and hence the slow down of acceleration is radical in the total hydraulic excavator. Therefore, the hydraulic rotation property is not sufficiently achieved by simple speed control and the uncomfortableness remains in the operation.